advisoryInfo-plain.xhtml has a <h:outputLink> pointing to repo-plain.xhtml which does not include the "id" parameter, which results in an error when the link is followed:
Error reading 'percentComplete' on type org.rhq.enterprise.gui.content.RepoDetailsUIBean
The fix is simply to add the missing parameters

I applied James patch to master commit id: 970715c
I was unable to test this as I cannot find the advisory pages and reproduction steps are missing. Discussed with the group and will check in patch anyway. The patch will not be picked to JON 3.1.1 until test steps are confirmed.

That's an area of JON I don't know well, so I'm not sure how to get there in the UI. Basically you need to view an advisory (advisoryInfo-plain) and then follow the link to the repo it's from.
The bug was fairly obvious, so was easy to fix without being able to test it.